This patch from Sami Farin lets you specify --fsync if you want fsync()
to be called on every file we write.

To use this patch, run these commands for a successful build:

    patch -p1 <patches/fsync.diff
    ./configure                         (optional if already run)
    make

based-on: 1ddcdaf3f6808ba53aef9e19f630a18808de22ac
diff --git a/options.c b/options.c
--- a/options.c
+++ b/options.c
@@ -48,6 +48,7 @@ int append_mode = 0;
 int keep_dirlinks = 0;
 int copy_dirlinks = 0;
 int copy_links = 0;
+int do_fsync = 0;
 int preserve_links = 0;
 int preserve_hard_links = 0;
 int preserve_acls = 0;
@@ -382,6 +383,7 @@ void usage(enum logcode F)
   rprintf(F,"     --partial-dir=DIR       put a partially transferred file into DIR\n");
   rprintf(F,"     --delay-updates         put all updated files into place at transfer's end\n");
   rprintf(F," -m, --prune-empty-dirs      prune empty directory chains from the file-list\n");
+  rprintf(F,"     --fsync                 fsync every written file\n");
   rprintf(F,"     --numeric-ids           don't map uid/gid values by user/group name\n");
   rprintf(F,"     --timeout=SECONDS       set I/O timeout in seconds\n");
   rprintf(F,"     --contimeout=SECONDS    set daemon connection timeout in seconds\n");
@@ -625,6 +627,7 @@ static struct poptOption long_options[] = {
   {"no-timeout",       0,  POPT_ARG_VAL,    &io_timeout, 0, 0, 0 },
   {"contimeout",       0,  POPT_ARG_INT,    &connect_timeout, 0, 0, 0 },
   {"no-contimeout",    0,  POPT_ARG_VAL,    &connect_timeout, 0, 0, 0 },
+  {"fsync",            0,  POPT_ARG_NONE,   &do_fsync, 0, 0, 0 },
   {"rsh",             'e', POPT_ARG_STRING, &shell_cmd, 0, 0, 0 },
   {"rsync-path",       0,  POPT_ARG_STRING, &rsync_path, 0, 0, 0 },
   {"temp-dir",        'T', POPT_ARG_STRING, &tmpdir, 0, 0, 0 },
@@ -2030,6 +2033,9 @@ void server_options(char **args, int *argc_p)
 			args[ac++] = tmpdir;
 		}
 
+		if (do_fsync)
+			args[ac++] = "--fsync";
+
 		if (basis_dir[0]) {
 			/* the server only needs this option if it is not the sender,
 			 *   and it may be an older version that doesn't know this
diff --git a/receiver.c b/receiver.c
--- a/receiver.c
+++ b/receiver.c
@@ -40,6 +40,7 @@ extern int relative_paths;
 extern int preserve_hard_links;
 extern int preserve_perms;
 extern int preserve_xattrs;
+extern int do_fsync;
 extern int basis_dir_cnt;
 extern int make_backups;
 extern int cleanup_got_literal;
@@ -322,6 +323,12 @@ static int receive_data(int f_in, char *fname_r, int fd_r, OFF_T size_r,
 		exit_cleanup(RERR_FILEIO);
 	}
 
+	if (do_fsync && fd != -1 && fsync(fd) != 0) {
+		rsyserr(FERROR, errno, "fsync failed on %s",
+			full_fname(fname));
+		exit_cleanup(RERR_FILEIO);
+	}
+
 	sum_len = sum_end(file_sum1);
 
 	if (mapbuf)
diff --git a/t_stub.c b/t_stub.c
--- a/t_stub.c
+++ b/t_stub.c
@@ -21,6 +21,7 @@
 
 #include "rsync.h"
 
+int do_fsync = 0;
 int modify_window = 0;
 int module_id = -1;
 int relative_paths = 0;
diff --git a/util.c b/util.c
--- a/util.c
+++ b/util.c
@@ -25,6 +25,7 @@
 
 extern int verbose;
 extern int module_id;
+extern int do_fsync;
 extern int modify_window;
 extern int relative_paths;
 extern int preserve_times;
@@ -344,6 +345,13 @@ int copy_file(const char *source, const char *dest, int ofd,
 			full_fname(source));
 	}
 
+	if (do_fsync && fsync(ofd) < 0) {
+		rsyserr(FERROR, errno, "fsync failed on %s",
+			full_fname(dest));
+		close(ofd);
+		return -1;
+	}
+
 	if (close(ofd) < 0) {
 		int save_errno = errno;
 		rsyserr(FERROR_XFER, errno, "close failed on %s",
